Since Yitzhak mentioned me, yes, we had the same problems with the NVidia cards. Got no answer to our needs, couldn't work on the driver ourselves and had to move forward, so we used other brands and now a new multiterminal solution (multiXnest) that is more hardware independent.
But still, if NVidia could get this solved, there certainly would be a lot of interested people. We developed a Debian based distro that will be installed in all schools of the State of Paraná, Brazil. It will use 4-head terminals. Right now, the State is buying 33.000 (thirty tree tousand) PCI video cards. NVidia will not be accepted because of this problem, unless it is solved.